Armed Bear Common Lisp is distributed under the GNU GPL with Classpath exception. It was originally created as a component of the Armed Bear J editor, where it serves as an extension language (rather like Emacs Lisp for Emacs). It is now maintained as a standalone implementation.

ABCL runs quite well with SLIME, which allows you to run ABCL from within Emacs.

Portability

Armed Bear Common Lisp requires Java 1.5 or later. It runs much better with a JVM that features a JIT, such as (for Linux/x86) the IBM or Sun virtual machines. It also runs, though very slowly, with the GNU gij virtual machine, as of version 3.3, and (with some exceptions) with SableVM as of version 1.0.9. It is also possible to use recent versions of the GNU Java compiler gcj to produce a standalone native executable.

Accessing Java from ABCL

ABCL gives you access to all those methods in the Java
runtime environment. This is implemented using the Java Reflection
API. To call a static method, use the jstatic function:

To invoke a constructor, use jconstructor and jnew in place of jmethod and jcall.

(jnew (jconstructor "java.lang.Object"))

There are a fair number of (poorly) documented Java specific Lisp extensions in the JAVA package.
Currently, reading the source to 'java.lisp' while experimenting with the REPL is probably the best way to come to an understanding of what is available.

Of common interest is the JAVA:JINTERFACE-IMPLEMENTATION function, which allows one to implement a Java interface in Common Lisp.

Extensions

Alan Ruttenberg's JSS provides a more convenient syntax for calling Java. It is now packaged with the distribution as part of ABCL-CONTRIB.